Ryzen mem/uclk/fclk oopsie!

[Tee Hee Johnson]

Hello, I used to be right into overclocking and these days I cant really be bothered.

So with the 5800X and some 3600Mhz RAM all I done was set the XMP profile for the RAM so it would run at 3600Mhz and the nicer timings.

BUT the 5800X fclk (infinity fabric) is 1900Mhz and since I set the XMP to 3600Mhz for the RAM (1800Mhz) and left the rest on auto, the uclk and fclk were brought back down to the 1800Mhz of the RAM.

It's been running like that for months, I didnt even think of it. I guess it keeping all 3 at the 1800Mhz was nicer since Ryzen likes the 3 matched but by that it was underclocking itself.

Just something to be weary of, might as well check that with XMP set it isnt pulling the rest of the system down!

(CPU-Z bench moved from 6638.2 (average of 3 runs) to 6689.8 (average of 3), big whoop I know, but shows it makes a difference and likely more elsewhere)

 

[alec]

XMP set it isnt pulling the rest of the system down

In this case motherboard was smarter than you, running mem/uclk/fclk in sync is definitely the fastest mode. It is not underclocking.
Wouldn't trust differences less than 100pt in cpuz multicore. It is too sensitive to smallest background activity.
And I bet cinebench will not change. And I bet game benchmarks will prefer the sync mode.

But it does open a door to overclocking your memory a bit. Keep the memory in XMP mode, give it 0.05V more and try running it at 3800/1900 mode. It will be a win/win with added win for slightly lower latency

 

[Destination]

Indeed for 3600mhz mem run at 1800

 

[Tee Hee Johnson]

Well having the fclk running at 1800mhz rather than 1900mhz is technically underclocking.

I have done that, all 3 are now running at 1900mhz... well 3800, 1900, 1900.

 

[DarkBahamut]

Stock fclk isn't 1900, it's actually 1600. This is inline with AMD stating that zen 3 has a recommend memory clock of 3200.

1900 itself is quite high. My 5950X can't even POST above 1866 fclk, so you have a fairly decent CPU if it's nice and stable at 1900 (no WHEA errors logged, etc).

 

[opethdisciple]

Well having the fclk running at 1800mhz rather than 1900mhz is technically underclocking.

I have done that, all 3 are now running at 1900mhz... well 3800, 1900, 1900.

It's under clocking but will probably result in overall faster outcome. It's the correct thing to do running it in sync. So memory frequency / 2 = fclk.

Your motherboard did it for you.

It's a well know fact that if you run your memory and fclk out of sync you incur a latency penalty. It was around 10ns on the 3000 series.